The present invention relates to radio frequency (RF) communication receivers, systems and methods employing ultra wide bandwidth (UWB) signaling techniques. More particularly, the present invention relates to the systems and methods that use UWB transmissions to track the movement of remote devices by determining those devices' movement, direction, and distance with respect to a central device. Even more particularly, the present invention relates to systems and methods that use both RF transmissions and UWB transmissions in the same device.
It is desirable in many environments to be able to monitor the location or movement of a remote device from a fixed local device. For example, retail stores may wish to monitor their merchandise; warehouses or cargo transports may wish to keep closer track of the cargo that they handle; and internal communications networks may wish to keep track of what users are in which location. Thus, a variety of devices have been used to determine location and distance.
An example of such a device is an RF identity tag, e.g., as described in U.S. Pat. No. 5,995,006, to Walsh, U.S. Pat. No. 6,107,910, to Nysen, or devices of a similar design. Such an RF identity tag has RF circuitry that can detect RF signals transmitted by a local device (whether fixed or mobile) and can then reply with an RF signal of its own to send information back to the local device. The RF signal in this case is a data signal modulated by being impressed upon another RF carrier signal.
The present inventors have also presented a system and method for using UWB signals to achieve similar functions, as set forth in U.S. Ser. No. 09/685,202, for “METHOD AND SYSTEM FOR ENABLING DEVICE FUNCTIONS BASED ON DISTANCE INFORMATION,” filed Oct. 10, 2000. The UWB signal in this case is preferably one that approximately matches its bandwidth to its center frequency, as defined below.
One important aspect of remote devices such as these is their useful lifetime. If a receiver is used in a remote device, the device may have a limited power supply, e.g., a battery. In this case, it is desirable to minimize the use of the power source so as to extend its usable lifetime.
Some RF tags operate without a separate power supply. Instead they use the RF signal they receive to power themselves up and perform their desired function, e.g., having the incoming RF signal charge a capacitor. This is not possible with current UWB designs. While UWB transceivers may use low amounts of power they cannot use a power source capacitively charged by an incoming RF signal. However, the UWB tags proposed by the current inventors offer better reliability in cluttered environment, as well as other significant advantages.
It would therefore be desirable to provide a system that includes the advantages of both designs, while limiting their limitations.